MOS field-effect transistors with very thin silicon dioxide based gate dielectrics may experience unacceptable gate leakage currents. Forming the gate dielectric from certain high-k dielectric materials, instead of silicon dioxide, can reduce gate leakage. When conventional processes are used to form such transistors, a silicon dioxide transition layer may form between the high-k dielectric and the substrate. The presence of that transition layer may unfavorably contribute to the overall electrical thickness of the gate dielectric stack.